Attempts at utilizing-an optical fiber for the purpose of for example sensing a liquid and detecting the concentration of that liquid have been known.
As one type of sensor utilizing an optical fiber, a “hetero core” type optical fiber sensor comprised of an optical fiber at the middle of which a portion of a different core diameter known as a “hetero core” is melt bonded is known. By providing this hetero core, it becomes easier to generate interaction between light used for the sensing and the outside of the sensor.
For example, Patent Document 1 discloses an example of a hetero core type optical fiber sensor.
In Patent Document 1, a hetero core is melt bonded to the front end of an optical fiber. Then, the optical fiber side end of this hetero core type optical fiber sensor at the front end of which the hetero core is bonded is connected to an OTDR (Optical Time-Domain Reflectometer).
By making light strike the hetero core type optical fiber sensor from the OTDR and measuring an intensity of backward scattered light generated in the hetero core by the OTDR, the presence of a liquid, the concentration of the liquid, or other aspects of the state of the external environment can be detected in accordance with the change in intensity of the backward scattered light.
Patent Document 1: Japanese Patent Publication (A) No. 2002-350335 (FIG. 4)
Non-patent Document 1: Kasai, “Bio-sensor utilizing Surface Plasmon Resonance (SPR)” Protein Nucleic Acid Enzymes, vol. 37, no. 15 (1992) pp. 2977-2984